Open Street Maps – What are they and why use them?

Open Street Map

Below I’ll try to explain Open Street Map and why it’s important to have various open sources for data such as maps! This post is mainly made of up excerpts from

On the Open Street Map Wiki page OSM is defined as “the project that creates and provides free geographic data and mapping to anyone who wants it. Most maps you think of as free actually have legal or technical restrictions on their use.”

Essentially this means that OSM is Wikipedia for maps where any user can add and edit maps plus the data is freely available for anyone to use (commercial or non-commercial).

 How it works for mappers:

A mapper creates an account with The using the Edit button then gets presented with two options:

  • Edit with Potlatch 2 –an in browser flash based editor (easiest to use for new users)
  • Edit with Remote control – a java based desktop editor (bigger learning curve and slightly more technical)

Screenshot of Potlatch 2: Flash based Map Editor. You literally trace the Arial imagery onto the map.


There are a variety of forms of gathering data for OSM(more details here):

  1. GPS – This is currently the most common way of gathering data for OSM, and often preferred or even essential for collecting the initial geometry of roads, paths and other ways.
  2. Local knowledge – Perhaps the best source of data is when you simply happen to know the area very well, and thus for example the names of the roads, shops etc. If the basic road layout is already present, you often don’t need any technical devices and can start straight away.
  3. Tracing maps using Aerial imagery (imagery mainly provided by Bing Maps under agreement)
  4. Photography or drawings
  5. Data may already be collected that requires people to convert it into a map. See local and global mapping projects.
  6. Seeing mistakes in a map and fixing them. There are a number of Quality Assurance tools which can be used to find problem areas.

Who cares?

An abridged version of the FAQ page on the OSM Wiki is below.

Why don’t you just use Google Maps/whoever for your data?

Because that data is copyrighted and owned by multiple organisations like the Ordnance Survey. Google/whoever just licenses it. If we were to use it, we’d have to pay for it. There’s also the potential that Google could introduce adverts etc in exchange for using their maps.

Who owns OpenStreetMap?

You do. The data and software is owned by you, the contributors.

Compare OSM and Google Maps side by side.

Who Uses OSM?

The growing list of names now includes Foursquare, Wikipedia and Apple (though there’s some debate over just how much OpenStreetMap data Apple uses in its glitchy maps, as it also lists TomTom as a provider). Craigslist also chose to use OSM for its own new built-in maps views, but never used Google to begin with.

In summary

As a user of maps, I hadn’t really given it much thought before now but now that I have been learning about the differences in the technologies I think it’s important and great to have an open source map data alternative which is freely available to people and  commercial programmes alike.